High-frequency oscillatory apparatus



Feb., 13, 1951 c. E. BEssEY 2,5@9739 HIGH-FREQUENCY oscILLAToRY APPARATUS Filed Jan. 15, 1945 2 sheets-sheet 2 Patented Feb. 13, 1951 UNITED STATES PATENT OFFICE HIGH-FREQUENCY OS CILLATORY APPARATUS Carlton E. Bessey, Red Bank, N. J.

Application January 15, 1945, Serial No'. 572,914

(Cl. Z50-36) 9 Claims.

The present invention relates to electric systems, and more particularly to oscillatory Asystems. From a more specic aspect, the invention relates to high-frequency systems.

An object of the invention is to provide a new and improved electric system of the abovedescribed character.

A further object is to provide a novel radiof-requency generator, adapted for use with either ordinary or ultra-high frequencies.

A further object still is to increase the frequency stability.

Another object is to obtain a higher frequency range than is attainable with conventional systems employing the same or similar equipment, such as the vacuum tubes.

Another object aim-s to increase the plate efficiency for the same frequency spectrum.

Still another object is to provide a system of the above-described character that shall be com pact, simple of construction, mechanically rigid, eiicient .and inexpensive.

The invention will now be more full-y explained in connection with the accompanying drawings, in which Fig. 1 is a circuit diagram embodying the invention in preferred form; Fig. 2 is a similar diagram, but simplied, and With parts omitted, in order to clarify the description;` Figs. 3 and 4 are views similar tol Fig. 1 of modifications; Figs.

5 and 6 are expanatory curves; and Fig. 7 is an I explanatory graph.

An oscillator is shown comprising a vacuum or electron tube 2 having a cathode 4, indirectly heated by a lament IIi, a control-grid electrode 'I and an anode or plate 8. Other types of cathode 4 may, of course, be employed.; for example, the directly-heated type illustrated in Fig. 4. The filament 6 is supplied with heating current from any desired energy source (not shown) by lead conductors I8, preferably crossed and intertwined, as shown, to reduce losses.

This oscillator, for convenience, maybe termed a first oscillator. It comprises an output or plate circuit and an input .or grid circuit. The firstv part of the output and the input circuits is they same. It may be traced from the cathode `4', by way of conductors I2 and I4 (shown. continuous in Fig. 2, but connected through grounds 58 in other figures), throughan energizing platesupplyB battery I6 and, by way of acondu'ctor I8, to a terminal 2li. In Fig. 2, the terminalz is shown grounded ,at 22, through a large Icy-pass condenser 2.4, by way of a conductor 25. In Figs. 1 and 3, the connection of the conductor 25-tothe ground ,22, is shown by way of an intermediate conductor I2 and the ground 50 in Fig. 4. From the terminal 20, the said first part of the output and input circuits continues, by way of a conf ductor 26, -grounded through its connection to the grounded terminal 20, to a similarly grounded xed terminal 281 of a conducting impedance element 38. The terminal 2-8 is replaced b-y a terminal 21'2 inFig. .4..

From the grounded terminal 28, in the systems oi Figs. l, 2 and 3, the output circuit is. completed, through an output-impedance portion 32 of the impedance element 30, to aiXed terminal 34 thereof and, by way of a conductor 38', to the anode 8. The remainder of the input circuit may be traced from the grounded terminal 28, through an input-impedance portion 38 of the impedance element' 3U, to an adjustable terminal 40 thereof; from the adjustable terminal 40, through a gridcoupling condenser 42,` the function of which is to prevent thevoltage of the battery It from being applied directly to the control electrode 7, to a terminal 44; and from the terminal 44, by Way of a conductor 46, tothe control electrode 'I. A grid resistor 48, connected between the terminal 44 and the ground 22, serves as a bias for the input circuit. A choke coil 49 (Fig. 4), of large impedance at the resonant frequency of the oscillator, may be connected in series with the bias resistor 48 to reduce the shunting eiiect of' this resistor 48 on the resonator circuit.

The conductor I4 may be connected adj-ustably `to a conventional one-quarter-wavelengthmatching cathode-tuning stud-tube l54 forenclosing the -lainent 'lead conductors I8. This variation ofthe inductance the -lament circuit is desirable when extremely high frequencies are employed.

For convenience, because of the sequence shown, the, xed terminals 34 and y28 and the adjustable terminalE 48' will hereinafter Lbe referredl toy as first, second and third terminals, respectively. Theoutputci-rcuit is therefore connected between thel first and; second terminals, and the input circuit between the second and third terminals.

Itwil-l be observed that the portion 32 of the impedance-element 3l) is connected in the output circuit `of the oscillator, between the cathode 4' andy the anode 8; and that the portion 38 of' the' 3 impedance element 3|] is connected in the input circuit, between the cathode l and the control electrode As these impedance parts 32 and 38 are inductive, therefore, this oscillator is of the ultra-audion or Colpitts type. The feed-back circuit involves the anode to the cathode and the grid to the cathode. Oscillations may therefore be produced through proper choice of the values of these impedances and the other parameters of the oscillator.

The parameters are properly chosen to start with, and final adjustments may be made by adjustment of the third terminal 50. For a particular tube 2, there is a particular optimum plate dissipation, as determined by the manufacturer of the tube. The third terminal E should be so adjusted that the tube shall not operate beyond its rated capacity. The maximum allowable radio-frequency potential will then be had at the rst terminal 3d.

If the third terminal d@ should be continuously adjusted away from its optimum position, toward the second terminal 23, for example, the grid 'i would receive less and less voltage; this follows from the fact that, as the second terminal 28 is grounded, it is at Zero voltage. If, on the other hand, the third terminal l should be adjusted away from its optimum position in the opposite direction, too great a drive would be impressed upon the grid l, with the resulting dissipation of too much power in the input circuit of the tube 2.

The impedance element St contains also an output-impedance part |32 and an input-impedance part |38, corresponding, respectively, to the output-impedance part 32 and the inputimpedance part 33, and respectively connected in the output and the input circuits of a second ultra-audion or Colpitts-type oscillator. The second oscillator comprises a vacuum or electron tube |62 having a cathode HB4, heated by a filament lli, a control-grid electrode lill and an anode or plate |88. The second oscillator is substantially the same as the first oscillator, andv the same reference numerals are therefore applied thereto, though augmented by illll. The same battery I6 is shown supplying the plate voltage of the second oscillator, through connecting a ground |58 to the ground 5|). The conductor |8 and the terminal 26, therefore, may be common to the output and the input circuits of the two oscillators. The output circuit of the second oscillator is connected between sequentially arranged fo irth and fifth xed terminals |34 and |28 of the impedance element 3|), corresponding to the rst and second fixed terminals 31| and 28. The input circuit of the second oscillator is connected between the fifth terminal |28 and an adjustable sixth terminal |40, the latter corresponding to the adjustablethird terminal 4G.

Where tuning over a wide frequency spectrum is desired, a variable condenser 35 may be connected between the terminals 34 and |315. The function of the by-pass condenser 2li is largely to maintain the terminals 23 and |28 at ground radio-frequency potential, in the event that unbalanced conditions should arise in the oscillatory circuit, and to prevent any radio-frequency energy or standing waves from becoming impressed upon the battery circuit; also to eliminate harmonics.

It will be observed that the impedance element 30 is continuous, as it closes in upon itself, and does not have any free ends. The resonator of the present invention may, therefore, be referred to as of the re-entrant type. It is shown diagrammatically in Figs. 1, 2 and 4, as an inductance winding coiled into the form of a toroid. The beginning and the end of the inductance winding are connected together, so as to coincide, thereby forming a continuous winding each turn of which has magnetic linkages with the adjacent turn on either side.

The oscillatory system of the present invention, therefore, comprises two oscillators, so connected symmetrically, in cascade, through the continuous impedance 32, that the output circuit of each oscillator shall be coupled to, so as to feed into, the input circuit of the other oscillator. The impedance element 3% thus constitutes a continuous transformer. The output energy in the output-impedance part 32 of the first oscillator' will therefore be induced by transformer action in the input-impedance part |38 of the second oscillator, and the output energy in the outputimpedance part |32 of the second oscillator will be induced by transformer action in the inputimpedance part 38 of the first oscillator.

With the connections above described, it is possible to have the various parts of the impedance element 3d in proper phase for attaining this end. This may be understood by referring to the graph of phases illustrated in Fig. 5, which represents a simplified form of the impedance element 3G, shown, not as a continuous element, but as a straight-line two-ended conductor one wave-length long, supporting a standing-voltage wave between its two ends 23, 23. The second and the fifth terminals 28 and |28 are there shown at the same zero or grounded potential. The rst and the fourth terminals 3d and |34, as indicated by the corresponding ordinates of Fig. 5, should be at maximum radio-frequency potential, but of opposite sign, and substantially degrees out of phase with respect to the phase of the terminals 23 and |28. The adjustment of the rthird and the sixth terminals il@ and Ill should be such as to provide proper grid drive for the tubes 2 and IGZ. The potential of the terminal All will be between the zero or ground of the terminal 2S and the potential of the terminal |34; and the potential of the terminal It!! will be between the Zero or ground of the terminal |23 and the potential of the terminal 3d, of'

substantially opposite phase to that of the terminal |35. If the phase angle of the input circuit should happen not to be of the right Value, that may be readily corrected for by adjustment, as of the cathode tuning stud 5. The grid-coupling condensers 412 and |5l2 should so couple theV respective grids l and lill of the tubes 2 and |92, respectively, to the terminals lll and |46, as to attain the proper voltage and phase relations for the grid drive of these two tubes.

Using point |28, for example, as a reference point, and progressing around the resonator in a clockwise direction, a point or terminal will be reached where the grid l of the vacuum tube |2 may be attached to provide proper excitation for the vacuum tube HB2. The next point or terminal thus progressively reached will be the point 3d, which is connected to the plate 8 of the vacuum tube 2, etc.

In operation, the filaments 6 and I are first connected to their energy sources, to heat them. After the cathodes l and ld have reached the proper temperature for normal emission, the plate-supply battery I6 is connected into the output circuit. Assuming that the oscillator 2 starts oscillating first, the radio-frequency energy thus produced will travel around the impedance element 35, due to transformer or inductive action. After leaving the output circuit of' the tube 2, this energy will be impressed on the input circuit of the tube m2, which will amplify and then re-impress it upon the resonator circuit. The resonator circuit will then carry the energy around to the grid circuit of the tube 2 which, in turn, Will build it up still further. This instantanecus build-up of the energy reaches a point Where the Q of the circuit is the only limiting factor of the radio-frequency power proe duced.

If the Wave form of Fig. 5 strictly depicts the true state of affairs accurately, the system will be free of harmonics, and the impedance 3|) will resonate at the frequency for which it may be designed. The continuous impedance element i may therefore be termed a continuous electric resonator, and the output and input circuits of the oscillators constitute a portion of this resonator. The term resonator is more appropriate than impedance because the element 30 does not really oifer any impedance to the flow of electric energy therethrough at the resonant frequency of the oscillatory system. The oscillatory circuit for each tube is a segment of the resonator. The wires connecting the platesupply voltage to the tubes are usually not considered part of the oscillatory circuit, inasmuch as they are at ground or radio-frequency potential. The tubes are connected to these segments in such manner that, in progressing around the resonator, the output circuit of each oscillator is followed by the input circuit of the other oscillator. the continuous resonator 30 by reason of the fact that the output of each oscillator is coupled to the input of the other oscillator. The electric tubes 2 and |532 are so connected to the impedance element 3S, at the points of connection of opposite phase, that changes in polarity in the rotating field arriving at one of the two points of connection produce amplified changes in polarity at the second point substantially in phase with the field arriving at the second point. The intensity of the rotating field is thus increased, and its rate or period of rotation is sustained.

For use at high frequencies, the conductors 36 and |35 should be short. The diagram of Fig. 5 would not otherwise apply, and harmonics would be introduced through the presence of standing Waves in these conductors. With long conductors 36 and |36, moreover, considerable losses might occur.

For very high frequencies, it may be desirable to employ one type of tube 2 or |02 rather than another; for example, the acorn tube. It has nevertheless been found that almost any conventional type of tube may be employed, even at the high frequencies, and beyond the cut-offfrequency rating specified by the manufacturer. Experience Shows, for example, that it is possible to attain as much as thirty per-cent higher frequencies, for a given tube, than the manufacturer of the tube states to be possible when connected into a conventional circuit. This is an indication of the much greater efficiency that is obtained with the circuit of the present invention.

The superiority of the continuous-type resonator of the present invention over conventional resonators will be appreciated further when it is reflected that the magnetic field is concentrated Within the resonator, thereby reducing eddycurrent loss. It is therefore possible to shield A rotating electric field is produced in the resonator without introducing an appreciable loss in efiiciency. The physical size of the resonator is much smaller than the size of conventional resonators designed to operate at the same frequency. Radiation losses are therefore reduced to a minimum.

The conductor 3U of Fig. 5` is shown in Fig. 6 bent into continuous circular form, with the end terminals 23, 2S connected together. Though Fig. 6 does not show so clearly as Fig. 5 that the terminals 28 and |28 are at zero radio-frequency potential, and the terminals 34 and |34 at maximum radio-frequency potential, with a phase difference of 180 degrees, it is digrammatically more like the impedance element 30 already described. In actual practice, the impedance element 3|) may be of Wire, coiled, as before stated, into the form of a toroid, or doughnut shaped, as diagrammatically shown in Figs. 1, 2 and 4. This makes for compactness and lower cost, besides reducing the amount of radiation from it. As the doughnut structure is open, some radiation will nevertheless take place therefrom. The resonator, however, may be not only a toroid, as represented at 30, but also a coaxial ring |56, a cylinder, a sphere, and so on. In all cases, the rotating electricy field. before mentioned will be guided along a sub-- stantially circular electric path.

A greater degree of freedom from radiation loss: may be obtained with the apparatus of Fig. 3,v in which the impedance element 3i! is shown replaced by a concentric-line resonator |55, Which determines the frequency. The connections are very much the same as those above described, except that the conductors 36 and |36'l are shown connected directly to the inner con-- ductor |58 of the concentric line, instead of tol the Winding 3Q, as in Figs. 1, 2 and 4. The inner conductor |58 is shown containing the same lparts 32, 33, |32 and |38, and the same six terminals 34, 23, itil, |34, |28 and |40 already described. The outer conductor it!k of the concentric line serves as a perfect shield, preventing radiation from the inductance of the inner conductor; further, it absorbs no radio-frequency energy.

The present invention makes it possible also to employ amplitude modulation on very high frequencies, without the disadvantages attendant upon the presence of frequency modulation, as occurs with conventional oscillators.

The frequency of the continuous-cascade operation of the present invention is remarkably constant, even at very high frequencies. Sustained operation may be obtained with the circuit of the present invention, even though the plate voltage should be reduced far beyond the point where conventional circuits cease to oscillate. Reference may be made, for example, to Fig. '2, containing a graph of the resonant frequency of the circuit plotted against the plate voltage of an 801 tube of the medium-power class. In a run with the tube at a 1G0percent-rated plate voltage of 609, for example, 34.98 megacycles were obtained. The plate voltage was then reduced, by steps, to 1.5 volts, but the system continued to oscillate. No appreciable frequency change could be detected until the voltage was reduced from a normal 600 to 200. At the voltage of 200, conditions began to change. A change of 230i) per cent in plate voltage produced a change of approximately 0.1 per cent in resonant frequency. Another oscillator might have stopped oscillating at volts, but this oscillator continued to 7 function with a plate voltage of only 1.5. This demonstrates the elimination of the external fields and the reduction of the radiation result in a high-Q circuit.

For a given rise in ambient temperature, moreover, the length of the conductor contained in the toroid increases; and since the toroid is physically continuous, this increase causes the distance between adjacent turns to increase, with a resulting decrease in the inductance of the coil.

The increase in the length of the coil, on the other hand, causes an increase in the inductance. The net resultant change of inductance is small or negligible. Since the null points and the node points on the toroid are fixed in position, because of the manner of connecting the components of this system, no near-harmonic power can be generated. This feature contributes to the generation of more useable power than can be obtained from the use of conventional coils.

Owing to the mechanical rigidity and compactness of the oscillator of the present invention, as well as its high efficiency and its stability compared to the voltage characteristics, the oscillatory system of the present invention may be put to L many uses. It is shown in Fig. 1 as feeding oscillatory energy to a dipole antenna 13E, |2. The pole |63 of the dipole is connected by a conductor |64 to an adjustable terminal |66 of the resonator 30; and the pole |52, by a conductor |38, to an adjustable terminal |16. The terminal |66 is shown disposed between the fourth terminal |35 and the fifth terminal |28, and the terminal |10 between the first terminal 3ft and the second terminal 28. The terminals |66 and |13 should be 212 and 312 are consecutively at zero R. F. potential, with a time lag of 120 degrees.

The first part of the output and the input circuits of each oscillator is the same. It may be traced from the cathode d, 13d or 2131i of the respective tubes 2, |02 and 232, by way of the conductors I2, ||2 or 2|2, through the energizing plate-supply B battery I6 and, by way of the conductor I8, to the terminal |12, which is connected to the terminals 212 and 312.

The connections of the tube 2 to the resonator 3D are substantially the same as described in connection with Figs. 1, 2 and 3, the grounded terminal 28 of Figs. 1, 2 and 3 being replaced by the grounded terminal 212.

From the grounded terminal 212, the output circuit of the tube 2 is completed, through the portion 32 of the resonator 3G, to the fixed terminal 34 thereof and, by way of the conductor 3S, to the anode 8. The remainder of the input circuit may be traced from the grounded terminal 212, through the portion 33 of the resonator 33, to the adjustable terminal d0 thereof; from the adjustable terminal 413, through the grid-coupling condenser Q2, to the terminal 14; and from the terminal M, by way of the conductor 43, to the control electrode 1.

From the grounded terminal 312, the output circuit of the tube |32 is completed, through the portion |32 of the resonator 32, which is shown overlapping the portion 38, to the fixed terminal |34 thereof and, by way of the conductor |36, to the anode |38. The remainder of the input circuit of the tube |32 may be traced from the grounded terminal 312, through the portion |33 of the resonator 30, to the adjustable terminal |113 thereof; from the adjustable terminal les, through the grid-coupling condenser |32, to the terminal |654, and from the terminal ILM, by way of the conductor |36, to the control electrode |131.

From the grounded terminal |12, the output circuit of the tube 232 is completed, through a portion 232 of the resonator 3|), which is shown overlapping the portion |38, to a fixed terminal 233 thereof and by way of a conductor 236, to the anode 2113 of the tube 202. The remainder of the yinput circuit may be traced from the grounded terminal |12, through a portion 233 of the resonator, which is shown overlapping the portion 32, to an adjustable terminal 2d() thereof; from the adjustable terminal Mii, through a grid-coupling condenser M2, to a terminal 2M; and from the terminal 2114, by way of a conductor 246, to the control electrode 231 of the tube 232. A grid resistor 2%, connected between the terminal 243 and the ground 222, serves as a bias for the input circuit of the tube 2. The portion 232 of the resonator 33 is conshould be connected at points the right distance from the terminals |12, 212, 312, which are at ground potential, to produce proper matching for the feed-wire impedance.

It is not essential that the terminals |12, 212

- and 312 be grounded by Way of conductors corresponding to conductors 26 and |23; even if not so connected, they will still find their own grounds. The plate-supply voltage is shown ccnnected to the terminal |12. It could be connected to the terminal 212 or 312 without affecting the operation.

v The resonator is pulsed by each tube in turn, with a time-delay equivalent to 120 degrees. As

each tube delivers a pulse to the resonator, a

virtual ground appears at a point on the resonator approximately half way between the plate and the grid points of connection to the resonator. There are therefore three points of virtual grounds on the resonator, which appear and disappear as the tube connected to that segment, whichincludes this virtual ground point, delivers a pulse and then dies down. These three points of virtual ground therefore appear in rotation, with a time lag of 120 degrees.

The invention is not limited to the use of even the three-phase arrangement. Any desired number of oscillators may be embodied in the oscillatory system of the present invention, connected to the continuous resonator at symmetrically arranged points in such manner as to achieve the above-described continuous-cascade arrangement. The phase difference of the points of the continuous resonator at which n oscillators would be connected thereto would be S60/1L degrees, and the output circuit of each oscillator would be connected through'the continuous resonator to the input circuit ofthe next adjacently disposed oscillator. n

In all cases, since the vacuum tubes are connected across only a portion of the resonator, their internal capacitances are not the predominating tuning factors of the system.

The invention may be used also in meteorological work, radio-direction finding, very-high-frequency operations, radar, remote control of aircraft, the transmission and reception of telephony, as a submarine-detector, as a power source in microwave ground and aircraft communication, as a positive altimeter, in amplitude modulation, side-band transmission, and elsewhere. Because the system of the present invention does not respond to harmonics and, consequently, eliminates image response, it is particularly adapted for use in radio-receiving apparatus. The resonator may be utilized as an antenna tuning inductance, connected between the antenna and the receiving system.

A circuit that has vacuum tubes, working in an oscillatory condition, and the output circuits of which are connected or coupled to an antenna system, may be regarded as a transmitter. In order to utilize the system of the present invention for receiving purposes, the tubes may be prevented from oscillating, as by increasing the C bias or otherwise, With the possible exception of using the system with the feeble oscillations present for the reception of continuous-wave code transmissions by the beat system.

Other and further modifications will therefore occur to persons skilled in the art, and all such are considered to fall within rthe spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

1. An oscillatory system having, in combination, a continuous resonator provided, in sequence, with first, second, third, fourth, fifth and sixth terminals, the first and the fourth terminals being of substantially opposite phase, the second and the fifth terminals being grounded, an oscillator having an input circuit connected between the second and third terminals and an output circuit connected between the first and the third terminals, and an oscillator having an input circuit connected between the fth and sixth terminals and an output circuit connected between the fourth and sixth terminals.

2. An oscillatory system having, in combination, a resonator provided, in sequence, with first, second, third, fourth, fth and sixth terminals, the first and the fourth terminals being of substantially opposite phase, the second and the fifth terminals being grounded, an oscillator having an input circuit connected between the second and third terminals and an output circuit connected between the first and the third terminals, and an oscillator having an input circuit connected btween the fifth and sixth terminals and an output circuit connected between the fourth and sixth terminals, the system being provided with an output circuit having a terminal connected between the first and the second terminals and a terminal connected between the fourth and the fifth terminals.

3. An oscillatory system having, in combination, a continuous resonator provided, in sequence, with first, second, third, fourth, fifth and sixth terminals, an oscillator having an input circuit connected between the second and third terminals and an output circuit connected between'the first and theY third terminals, and an oscillator having an input circuit connected between'the fifth andr sixth terminals and an output circuit connected between lthe fourth and sixth terminals.

4. An electric-system comprising a continuous single-element endless resonator having substantially uniformly distributed parameters and provided with a plurality of groups `of first, second and third terminals in sequence, a plurality of oscillators, one corresponding to each group of terminals, each oscillator having an input circuit connected between the second and third terminals and an-output circuit'connected between the first and third terminals of ;the corresponding group of terminals.

5. In combination, a continuous mechanically and electrically re-entrant resonator having substantially uniformly distributed inductance and capacitance, means electrically bonding together symmetrically spaced points on said resonator operative to render said points substantially equipotential and defining at least two sectors of the resonator, an electric discharge device having input and output electrodes, means connecting the input electrode to one sector of the resonator intermediate the spaced points defining the same, and means connecting the output electrode to another sector of the resonator intermediate the spaced points defining said last-mentioned sector.

6. In combination, a continuous mechanically and electrically re-entrant resonator having substantially uniformly distributed inductance and capacitance and electrical length at least equal to one wavelength at the natural resonant frequency of the resonator, means electrically bonding together symmetrically spaced points on said resonator operative to render said points substantially equipotential and defining at least two sectors of the resonator, an electric discharge device having input and output electrodes, means connecting the input of electrode to one sector of the resonator intermediate the spaced points defining the same, and means connecting the output electrode to another sector of the resonator intermediate the spaced points defining said lastmentioned sector.

'i'. In combination, a continuous, single-element, annular resonator having substantially uniformly distributed inductance and capacitance, means electrically bonding together symmetrically spaced points on said resonator operative to render said points substantially equipotential, and means connected to said resonator intermediate said spaced points operative to sustain in said resonator electromagnetic standing waves for which the electrical length of said resonator is at least one wavelength.

8. In combination, an endless annular toroidal coil having substantially uniformly distributed inductance and capacitance and having its turns wound continuously in the same direction throughout, means electrically bonding together symmetrically spaced points on said coil operative to render said points substantially equipotential and defining at least two sectors of said coil, an electric discharge device having input and output electrodes, means connecting the input electrode to one sector of the coil intermediate the spaced points defining the same, and means connecting the output electrode to another sector of the coil intermediate the spaced points defining Said last-mentioned sector.

9. In combination, an endless annular toroidal coil having substantially uniformly distributed 11 12 inductance and capacitance and having its tlrns UNITED STATES PATENTS Wound continuously in the same direc ion throughout, means electrically bonding together N111 ggegw Sileme Dec 13g-81939 symmetrically spaced points on said coil opera- 2911299 Ponn Aug' 13 1935 tive to render said points substantially equi- 5, 2141242 Georgi-211 Dec' 27 1938 potential, and means connected to said coil in- 2143658 Morris Jan 10 1939 termediate said spaced points operative to sustain 2149387 Brown Mall .1 1939 in said coil electromagnetic standing Waves for 2156261 Evans *l Mas; 2 1939 which the electrical length of said coil is at least 2169358 110111119351; "Aug 15 1939 one Wavelength 10 2,410,387 Muener oct.' 29,I 1946 CARLTON E' BESSEY- 2,415,977 Turner Feb, 18, 1947 2,434,474 Strutt Jan. 13, 1948 REFERENCES CITED The following references are of record in the 

